Reinforcing fillers such as carbon black, silica have been conventionally used for reinforcing rubber. Silica, as compared with carbon black, has properties of a low tan .delta. at high temperatures (around to 60.degree. C.) and a high tan .delta. at low temperatures (around to 0.degree. C.), and therefore, when used for rubber compositions for tire treads, a tire having a low rolling resistance and a high gripping power can be advantageous produced. However, silica, is inferior to carbon black in wear resistance and has a low electrical conductivity, and therefore, if silica is used for tires, there is the problem that the tire will pick up a charge when driven on and will cause various problems. These and other problems have not been solved yet.
On the other hand, it has been proposed in, for if example Japanese Examined Patent Publication (Kokoku) No. 50-14254 and Japanese Examined Patent Publication (Kokoku) No. 7-30269 that, by coating the surface of a pigment etc. with, for example, silica the surface charge thereof is changed whereby the dispersibility is improved and the weather resistance is increased. For example, Japanese Examined Patent Publication (Kokoku) No. 7-30269 discloses a method for treating the surface of carbon black for a powder coating composition comprised of dispersing carbon black in water, adjusting the pH thereof to 6 or more, and, while maintaining the temperature of 70.degree. C. or more, using sodium silicate to cause amorphous silica to precipitate on the surface of the particles of carbon black. However none of these publications discloses the deposition of silica on the surface of the carbon black for reinforcing the rubber.
Further, various patents disclose the treatment of carbon black with silicon compounds.
For example, Japanese Unexamined Patent Publication (Kokai) No. 53-100190, Japanese Unexamined Patent Publication (Kokai) No. 56-38357, and Japanese Unexamined Patent Publication (Kokai) No. 61-291659 disclose the mixing and drying of a silicone compound and carbon black.
However, these prior arts do not refer to the superior properties in applications for reinforcement of rubber obtained by the formation of the composites of carbon black and silica.
Further, Japanese Unexamined Patent Publication (Kokai) No. 58-125249 discloses the mixing of carbon black coated with a silane coupling agent on the surface thereof to a thermoplastic resin, but this publication also does not describe anything regarding the superior properties when blending with rubber, in the same way as the above.
Japanese Unexamined Patent Publication (Kokai) No. 4-233976 discloses a process for producing a heated reaction product of a silicon compound having two or less silicone atoms in a molecule with carbon black as a carbon black chemically modified with an organosilicon compound and a rubber composition including the same. This is intended to provide, at the surface of the carbon black, various organic groups through alkoxysilyl groups. The deposition of silica on the surface of the carbon as in the present invention is a fundamentally different technical idea.